ESTRO 2023 - Abstract Book

S1594

Digital Posters

ESTRO 2023

Results We achieved the best possible CBCT imaging quality with the 120kV and 20mA setting parameters. This corresponds to the "HD3D (large)" O-Arm setting mode. With this, the image quality with artifact reduction, minimization of image noise and consideration of a low radiation exposure of only 0.5mSv for the patients is feasible. Approximately 15 additional minutes were accounted for contouring and planning times. Conclusion Good-quality intraoperative imaging can be obtained when performing IORT, easing the applicator positioning and resulting in a more precise target irradiation. Operating times would be minimally extended with this procedure. A clinical study will initiate based on these findings.

PO-1854 Dose escalation with integrated boost using high-field MR-LINAC in prostate cancer patients.

C. Onal 1 , G. Arslan 2 , C. Yavas 3 , E. Efe 3 , G. Yavas 3

1 Baskent Uiniversity, Department of Radiation Oncology, Adana, Turkey; 2 Baskent Universtiy, Department of Radiation Oncology, Ankara, Turkey; 3 Baskent University, Department of Radiation Oncology, Ankara, Turkey Purpose or Objective Previous research has shown that hypofractionated therapies and higher radiation doses provide superior biochemical control. We sought to assess the dosimetric feasibility of dose escalation to intraprostatic lesion (IPL) using high field MR LINAC in patients with localized prostate cancer. Materials and Methods The dosimetric data of 18 prostate cancer patients with low and intermediate risk who were treated with 36.25 Gy in 5 fractions were analyzed. Everyone was treated with a 1.5-Tesla Elekta Unity MR-LINAC. Four plans were generated: one with a dose of 7.25 Gy to the prostate and 1/3 of the proximal seminal vesicle with no integrated boost, and three with doses of 7.50, 7.75, and 8.00 Gy to the intraprostatic boost. The target volume coverage and organs at risk, such as the rectum, bladder, urethra, and femur, were compared in terms of doses. Plans were compared based on the maximum (D2) and minimum (D98) doses for prostate and IPL, as well as the homogeneity index. Results The prostate and IPL had mean volumes of 46.2 ± 18.6 cc and 12.5 ± 7.3 cc, respectively. The doses administered to the rectum and bladder was 65.0 ± 27.3 cc and 184.6 ± 132.1 cc, respectively. All plans met the dose constraints. D2 for prostate was 37.9 ± 0.2 Gy, 38.7 ± 0.2 Gy, 39.0 ± 0.2 Gy, and 41.3 ± 0.2 Gy, with statistically significant differences between each plan. However, there were no significant differences between plans in terms of D98 for prostate and D2 and D98 for IPL. The D1cc of the rectum for each plan was 35.2 ± 0.7 Gy, 35.1 ± 1.2 Gy, 35.1 ± 1.2 Gy, and 34.9 ± 1.7 Gy, with no statistically significant difference. The D1cc for the bladder was 37.0 ± 0.7 Gy, 36.9 ± 0.8 Gy, 37.3 ± 0.8 Gy, and 37.7 1.1 Gy for plans containing no SIB, 37.5 Gy, 37.75 Gy, and 40 Gy, respectively. The D1cc of the bladder was significantly greater in the SIB 40 Gy plan than in the SIB 37.7 Gy plan and the no SIB plan (p = 0.009 and p = 0.008, respectively). Other bladder